Xylem TB500 ONLINE TURBIDITY ANALYZERS - Manual (Page 22)

TB500 (2/07)
Rev. 1.0 18
7.4 Configuring the Alarms
Two relays are provided that are designed to operate as two independent programmable
alarms. Three types of information must be input to fully program each alarm:
1. The alarm function (HI, LO, or OFF)
2. The alarm set point (level at which the alarm activates)
3. The delay time for the alarm: the time that the set point must be exceeded prior to
alarm activation and the time before resetting the alarm(prevents ringing in the relay)
These three items are described below:
Alarm Function: The alarms can either be turned OFF or programmed to operate in one
of two different manners:
1. HI alarm: the relay changes state when the measured turbidity level is higher than the
programmed alarm level for a prescribed amount of time.
2. LO alarm: the relay changes state when the measured turbidity level is lower than the
programmed alarm level for a prescribed amount of time.
Note: The relays automatically change state when an internal system failure is detected.
Alarm Set Point: The level at which an alarm activates is called the alarm set point. On
the instrument, the alarm set point is designated as “S/P”. The set point is adjustable to
any valid turbidity level over the range of the instrument in steps of 0.01 NTU.
Alarm Delay Time: The alarm delay times are used to prevent ringing of the alarm when
the measured turbidity level is close to the set point. The function of the delay times is as
follows:
Delay On : The turbidity level must exceed the alarm set point continuously for at least
this number of seconds before the alarm activates.
If the delay on time is set at 5 seconds and the process turbidity exceeds the set
point continuously for only 4 seconds, the alarm will not be activated.
However, process turbidity exceeds the set point continuously for 5 seconds or
more, the instrument will activate the alarm.
Delay Off : The turbidity level must not exceed the alarm set point continuously for at
least this number of seconds prior to deactivation of the alarm.
If the delay off time is set to 5 seconds and the process has exited out of the
alarm condition, the alarm will be reset only if the process is out of the alarm
condition for a continuous 5 seconds. Otherwise, the instrument will still
signal an alarm condition.
7.4.1 Alarm 1
Alarm 1 Function:
The ALM1 is displayed and the display indicates the current function
of alarm 1 (HI, LO, or OFF). Use the
toru buttons to cycle through and select the
desired function. Press the
↵ button to accept the selection.
If the alarm was turned OFF a prompt will appear to set up alarm 2 (go to section 7.4.2).
If, on the other hand, one of the other functionalities was selected a prompt will appear to
set the delay times.